Tomato-based products such as tomato ketchups, barbecue sauces, pizza and pasta sauces and other similar condiments are typically made from tomato pastes, tomato purees, tomato juices or similar compositions that contain substantial amounts of tomato solids. These tomato solids include water-insoluble tomato particles, including tomato seeds and portions of tomato skins; and tomato fibres (cellulose, hemi-cellulose, pectin) which comprise the bulk of the insoluble tomato solids. Each of these components affects the stability, appearance, flavour and sensory appeal of tomato-based food products.
For example, the carotene lycopene that gives tomato sauce its characteristic red colour is found primarily in chromoplasts within the tomato pulp and tomato fibre. Hence, the amount and distribution of the pulp and fibre will determine whether the tomato sauce will have an overall, even desirable colour. In addition, the size and distribution of the tomato pulp particles may also affect the texture of such tomato-based products. Large, unevenly distributed pulp particles will tend to produce a lumpy product, while extremely finely divided pulp particles will tend to produce a smooth textured product.
Similarly, the tomato fibres tend to link together and intertwine to form a lattice network or fibrous matrix that provides body and viscosity to tomato-based products and further traps free liquid which would otherwise “weep”, i.e. separate, from the product. The liquid typically consists primarily of water and may also include other tomato fluids, and additives to the product. When present in sufficient concentrations, the pectin in tomato-based products forms a gel that also acts to bind free liquid in the products and to increase the products' viscosity.
It is known to modify the physical properties of the tomato solids in tomato sauces and slurries using various techniques, including homogenisation of the products. Homogenisation is employed to finely divide, break down and disperse pulp particles throughout a slurry to produce products with acceptable colour and texture. Tomato pulp contributes many relatively spherical particles, which are insoluble in water and which must be reduced in size and uniformly dispersed throughout the product. If this is not done, a product with an excessively rough texture will result. Furthermore, since the carotene pigment (lycopene) is contained in these particles of pulp and fibre, failure to properly disperse them will result in a product with poor uniformity and depth of colour.
In addition to the above particles, tomato dispersions have a very high content of fibrous strands. Through proper processing techniques, these fibres form a structure that is responsible for the viscosity of the product and for its ability to bind water. Homogenisation can be used to enhance the water binding capacity of the fibrous strands. This enhanced water binding capacity is usually reflected by increased product viscosity and/or reduced syneresis.
However, the process does have limitations. If too high a homogenizing pressure is used, then the fibre network will be broken down. Although the greater number of individual fibres will absorb more water and cause a greater viscosity increase, any remaining free water will quickly separate because the structure which bound this water will have been destroyed. In short, the price for greater viscosity is an increase in serum separation. In practice, processing conditions are chosen on the basis of a compromise between these two opposing effects. A component that plays an important role in the preparation of tomato dispersions is pectin. This naturally occurring polysaccharide increases product viscosity and reduces separation by tying up any remaining free water. Homogenization increases both of these effects by aiding in the enhanced and uniform solubilisation of the pectin.
Obviously, the preparation of tomato products is very much subject to variations in the structure and chemistry of the tomatoes used. This, in turn, is dependent upon such growing factors as: geographical location, climate conditions, weather variations, soil conditions, growing season and variety of tomato. There is no way to eliminate the influence of such factors. However, adjustments in homogenising conditions may be required to compensate for unwanted characteristics in the final product resulting from these factors. This type of precise control over the physical characteristics of the finished product is very important in maintaining a degree of consistency from batch to batch.
Alternative processing steps have been used to supplement the effects of homogenisation, including the additional steps of milling the products or using of vacuum expansion chambers to increase viscosity and improve the colour of the products.
Despite the efforts that have been made to optimise the stability, appearance, flavour and sensory appeal of tomato-based food products by manipulating the processing conditions that are employed in the manufacture of these products, it is common practice to employ additives, notably calcium chloride and/or viscosifiers, to further improve stability and texture of tomato-based products. In the tomato processing industry calcium chloride is frequently added to tomato products to increase their viscosity and to prevent syneresis. The calcium ions react with free carboxyl groups of tomato pectin to produce a gel network of calcium pectate.
Viscosifiers such a natural gums, starch, pectin, guar gum, xanthan gum and CMC are also widely used to increase the viscosity of and/or to prevent syneresis in tomato-based products such as ketchup. From a consumer perspective, the use of such additives in tomato products, notably the use of additives that are foreign to tomatoes, is undesirable.
Farahnakyi et al., Journal of Texture Studies, vol. 39. (2007), pp. 169-182 describe a method for preparing a thickening agent, involving drying tomato waste (“pomace”, mainly including tomato seeds and skins) to a moisture content of about 7%, followed by milling and sieving. This results in a tomato pomace tomato fibre powder comprising (on dry matter) 24.8 wt % protein, 0.08 wt % lycopene, 13.8/14.5 wt % reducing sugars/total sugars and 41.1 wt % fibers.
U.S. Pat. No. 7,166,315 describes a composition comprising dietary fibres with high water holding capacity (WHC) that is obtained from tomato pulp. The composition can be used as a texturing, bulking, viscosity controlling or syneresis-preventing agent for food. The US patent further describes a process for preparing the aforementioned composition comprising:    1) pre-treating tomatoes by conventional unit operations which comprise washing, sorting and crushing,    2) separating the peel and seeds of the tomato from the crushed tomatoes,    3) subjecting the crushed tomatoes to heat treatment (80-110° C.),    4) separating the crushed tomatoes into serum and pulp by centrifugation, to obtain fine pulp,    5) extracting carotenoids and lipids from the fine pulp obtained in step 4, and    6) drying the extracted fine pulp obtained in step 5;and wherein the peels and seeds of the tomato are separated from the crushed tomatoes at any stage before said extracting and drying. Following the separation stage, carotenoids and lipids are extracted from the fine pulp to obtain, after solvent removal, tomato fibres substantially free of lipids, carotenoids, seeds and peels The solvent may then be removed by azeotropic distillation.
WO 2011/138163 describes a process for preparing a tomato-derived thickening agent comprising the steps of:    a) providing a tomato pulp containing 3-15 wt. % tomato soluble solids (TSS) and 0.3-5 wt. % tomato insoluble solids (TIS);    b) isolating from said tomato pulp a tomato serum fraction having a reduced TIS content of less than 2.0 wt. % and a TSS content of at least 3 wt. %;    c) subjecting said tomato serum fraction to a filtration step to produce a retentate and a filtrate, said filtration step employing a membrane with a molecular weight cut-off (MWCO) in the range of 10-20,000 kDa;    d) collecting the retentate; and    e) optionally drying the retentate.
WO2008/148828 describes the isolation of a gel building material from tomato. 6.9 kg Red Matrix tomatoes were soaked for 60 seconds in boiling water. Skin, seeds and coarse were removed thereafter by hand. 4.4 kg fruit flesh were obtained. This flesh was homogenized in a kitchen blender and thereafter heat treated at 80° C. for 10 minutes. The homogenized flesh was cooled down to room temperature by the application of cool water and afterwards centrifuged at 5000 rpm (7268 g) for 10 minutes. The supernatant was discarded and the remaining cellular material was washed with 500 ml water. The resulting slurry was centrifuged again at 5000 rpm (7268 g) for 10 minutes. This washing step including the subsequent centrifugation was carried out in total 3 times.
The obtained cellular material was split into two fractions in a ratio of 2:1. ⅔ of the obtained cellular material was washed with 500 ml acetone p. a. followed by a centrifugation step at 5000 rpm (7268 g) for 10 minutes. This washing procedure in acetone as organic solvent was in total repeated three times. The obtained washed cellular material was then passed through a Buchner funnel equipped with a GF/A filter and again washed with more acetone as organic solvent. Afterwards the cellular material was dried under a fume hood to obtain 20.5 g CMW from Red Matrix tomatoes. The remaining ⅓ of the cellular material obtained after washing with water was subjected to the exact same treatment as described above, however with the difference, that ethanol (94%) was used instead of acetone. 10.7 g CMW from Red Matrix tomatoes were obtained.
Redgwell et al. (Physicochemical properties of cell wall materials from apple, kiwifruit and tomato, Eur Food Res Technol (2008) 227:607-618) describe a method of isolating cell wall materials (CWMs) from the fruit of ripe apple, kiwifruit and tomato which according to the authors maximised the water retaining capacity and viscosity generating properties of the CWMs. In this method fruit were peeled and the pericarp separated from the seeds and other tissues (i.e. core and locule tissue in kiwifruit and the locule tissue in tomato). Tissue was homogenised in a Waring blender with a little added water. The tissue homogenate was heated at 80° C. for 10 min to inactivate endogenous enzymes, cooled, centrifuged at 5,000 g for 10 min and the supernatant discarded. The residue (CWM) was re-suspended in 600 ml of water, centrifuged and the supernatant discarded. The water-wash of the CWM was repeated twice. CWM was resuspended in 600 ml acetone, centrifuged as before and the acetone supernatant discarded. CWM was resuspended in acetone a second time and filtered through glass fibre paper (GF/A). The cake of CWM was rinsed with further acetone on the filter, sucked dry and allowed to air-dry in a fume hood overnight.